mumble vs verbalize

mumble is a noun but verbalize is not a noun.

Word	Noun	Adjective	Verb	Adverb
mumble	Yes	No	Yes	No
verbalize	No	No	Yes	No

As verbs, verbalize is a hypernym of mumble; that is, verbalize is a word with a broader meaning than mumble:

Other hypernyms of mumble include mouth, speak, talk, utter, verbalise.

mumble (noun)	verbalize (noun)
a soft indistinct utterance

mumble (verb)	verbalize (verb)
talk indistinctly; usually in a low voice	convert into a verb
grind with the gums; chew without teeth and with great difficulty	express in speech
	be verbose
	articulate; either verbally or with a cry, shout, or noise